Question: Solve: $\dfrac{1}{4} + \dfrac{3}{5} - \dfrac{3}{10} = $
Let's look at the multiples of each denominator and see which multiples they have in common. Denominator Multiples ${4}$ $4, 8, 12, 16, \underline{{20}}$ ${5}$ $5, 10, 15, \underline{{20}}$ ${10}$ $10, \underline{{20}}, 30$ The least common multiple is ${20}$. Let's use multiplication to make each fraction have a denominator of $20$. $\begin{aligned} &{\dfrac{1}{4}}=\dfrac{{1} \times 5}{{4} \times 5} = {\dfrac{5}{20}}\\\\ &{\dfrac{3}{5}}=\dfrac{{3} \times 4}{{5} \times 4} = {\dfrac{12}{20}}\\\\ &{\dfrac{3}{10}}=\dfrac{{3} \times 2}{{10} \times 2} = {\dfrac{6}{20}} \end{aligned}$ $\begin{aligned} &{\dfrac{1}{4}} + {\dfrac{3}{5}} - {\dfrac{3}{10}}\\\\ =& {\dfrac{5}{20}} + {\dfrac{12}{20}} - {\dfrac{6}{20}}\\\\ =&\dfrac{5 + {12} - {6}}{20}\\\\ =&\dfrac{17 - 6}{20}\\\\ =&\dfrac{11}{20} \end{aligned}$ $\dfrac{1}{4} + \dfrac{3}{5} - \dfrac{3}{10} = \dfrac{11}{20}$